1. Field of the Invention
The present invention relates to an air flow system which includes a machine which compresses or conveys fluid and can be used as a compressor, pump or actuator.
2. Description of the Related Art
A known air flow system includes a machine which compresses or conveys fluid by making use of changes in the volume of a compression chamber formed by a movable body and the inner wall of a casing, the changes being brought about by movement of a movable body. The movable body consists of a diaphragm. Rotary movement of a driving shaft transmits reciprocation to a rod, and the rod transmits the movement to the diaphragm.
FIG. 4 is a characteristic graph for a conventional compression machine. According to FIG. 4, as the rotation speed of the drive shaft increases, the volumetric efficiency in the compression machine decreases, so that the volume of gas discharged per rotation decreases.
FIG. 7 is the air intake system of an engine 41 with a conventional supercharger. According to FIG. 7, the supercharger 42 is driven by the rotation of the engine, and the compressed charge is fed to the engine cylinder 41a, so that output power of the engine is increased. When the discharged pressure from the supercharger reaches more than a predefined pressure, an air bypass valve 34 opens and the excess pressure is bypassed or returned to a point upstream of the supercharger.
The intake system also includes an air cleaner 36, an air flowmeter 37, an idle speed control valve (ISCV) 38, an intercooler 39 and an injector 40.
FIG. 3 is the characteristic graph of the above-mentioned supercharger. According to this supercharger, as the rotation speed of the engine increases, the volume of gas discharged per rotation increases, and a great amount of excess pressure is generated at high rotation speeds.
Thus, on the one hand, there is the problem that as the rotation speed increases, the volumetric efficiency of a compression machine decreases and, on the other hand, that as the rotation speed increases, the discharge volume of a supercharger increases so that the excess discharge must be relieved and so is wasted.